in reply to Draw a line

Nowadays, most graphics toolkits already supply you with a function line_to or line, which draws the line for you, so I recommend that you read through the documentation of your graphics toolkit and find what the name and the usage of the corresponding function is.

If your graphics toolkit only has a set_pixel function and no line function, then using Bresenhams algorithm for drawing lines is most likely one of the fast methods to draw lines. Understanding how the algorithm works is also very rewarding, as the algorithm operates without floating point numbers.

If you are more looking for the general concept of drawing a line between two points, the drawing of a line between two points can be interpreted as finding all points (x,y) on the line passing through (x1,y1);(x2,y2) where x1 <= x < x2.

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Re^2: Draw a line
by eserte (Deacon) on Jun 03, 2004 at 10:45 UTC
    For lazy people, here's a perl implementation of this algorithm: 
            my($x1,$y1, $x2,$y2) = @_;
        use integer;
        my($dx, $dy, $incr1, $incr2, $d, $x, $y, $xend, $yend, $xdirfl
+ag, $ydirflag);
        $dx = abs($x2-$x1);
        $dy = abs($y2-$y1);
        if ($dy <= $dx) {
        $d = 2*$dy - $dx;
        $incr1 = 2*$dy;
        $incr2 = 2 * ($dy - $dx);
        if ($x1 > $x2) {
            $x = $x2;
            $y = $y2;
            $ydirflag = (-1);
            $xend = $x1;
        } else {
            $x = $x1;
            $y = $y1;
            $ydirflag = 1;
            $xend = $x2;
        }
        set_point($x,$y);
        if ((($y2 - $y1) * $ydirflag) > 0) {
            while ($x < $xend) {
            $x++;
            if ($d <0) {
                $d+=$incr1;
            } else {
                $y++;
                $d+=$incr2;
            }
            _set_point($x,$y);
            }
        } else {
            while ($x < $xend) {
            $x++;
            if ($d <0) {
                $d+=$incr1;
            } else {
                $y--;
                $d+=$incr2;
            }
            set_point($x,$y);
            }
        }
        } else {
        $d = 2*$dx - $dy;
        $incr1 = 2 * $dx;
        $incr2 = 2 * ($dx - $dy);
        if ($y1 > $y2) {
            $y = $y2;
            $x = $x2;
            $yend = $y1;
            $xdirflag = (-1);
        } else {
            $y = $y1;
            $x = $x1;
            $yend = $y2;
            $xdirflag = 1;
        }
        set_point($x,$y);
        if ((($x2 - $x1) * $xdirflag) > 0) {
            while ($y < $yend) {
            $y++;
            if ($d < 0) {
                $d+=$incr1;
            } else {
                $x++;
                $d+=$incr2;
            }
            set_point($x,$y);
            }
        } else {
            while ($y < $yend) {
            $y++;
            if ($d < 0) {
                $d+=$incr1;
            } else {
                $x--;
                $d+=$incr2;
            }
            set_point($x,$y);
            }
        }

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